1. Field of the Invention
This invention relates to filter assemblies. More particularly, this invention discloses triple-mode, mono-block resonators that are smaller and less costly than comparable metallic combline resonators, including a microwave flat delay filter.
2. Background of the Invention
When generating signals in communication systems, combline filters are used to reject unwanted signals. Current combline filter structures consist of a series of metallic resonators dispersed in a metallic housing. Because of the required volume for each resonator, the metallic housing cannot be reduced in size beyond current technology, typically 3–10 cubic inches/resonator, depending on the operating frequency and the maximum insertion loss. Furthermore, the metallic housing represents a major cost percentage of the entire filter assembly. Consequently, current metallic filters are too large and too costly.
Further, personal communication systems demand highly linearized microwave power amplifiers for base station applications. Feedforward techniques are commonly used in the power amplifier design for reducing the level of the intermodulation distortion (IMD). One component common to feedforward power amplifier design is the delay in the primary high power feedforward loop for canceling the error signals of the power amplifier (PA). The electric delay is typically achieved by the coaxial type transmission line or metallic resonator filter. A filter-based delay line can be thought of as a specially designed wide bandpass filter with optimized group delay
However, the related art has various problems and disadvantages. For example, but not by way of limitation, because of the required volume for the delay line/filter for the new generation communication systems, the coaxial line and metallic housing filter cannot be further reduced in size limited by maximum insertion loss.